add_langgraph_fastapi_endpoint clones the agent on every request, and
LangGraphAgent.clone() rebuilds it through type(self)(...) forwarding the base
class's own behavior flags. LangGraphAGUIAgent restated a closed keyword-only
signature, so ag-ui-langgraph 0.0.43 - which began forwarding
enable_legacy_on_interrupt_event, emit_interrupt_outcome and emit_raw_events -
made every request 500 on the documented LangGraph + FastAPI quickstart:
TypeError: LangGraphAGUIAgent must override clone() or ensure its __init__
accepts (name, graph, description, config) as keyword arguments:
LangGraphAGUIAgent.__init__() got an unexpected keyword argument
'enable_legacy_on_interrupt_event'
Our dependency is ag-ui-langgraph[fastapi]>=0.0.42 with no upper bound, so a
fresh install already resolves to 0.0.43 and fails on the first message.
__init__ now forwards **kwargs upstream instead of restating the base signature.
That fixes the 500 without waiting on an upstream release, and makes base flags
reachable at all - emit_raw_events=False, the OSS-607 payload opt-out, could not
be set by any CopilotKit user through this subclass.
Also constructs the intercepted-tool-call test double for real rather than via
object.__new__. That helper built an instance with no behavior flags set, so it
raised AttributeError out of the base dispatch path the moment ag-ui-langgraph
started reading one - 4 failures the pinned 0.0.42 lockfile currently hides.
Verified against published ag-ui-langgraph, both versions: 0.0.43 gives 235
passed / 11 skipped (was 4 failed, 226 passed), and 0.0.42 gives 233 passed /
13 skipped (the two flag tests skip by design). End to end, two sequential
POSTs through add_langgraph_fastapi_endpoint on 0.0.43 return HTTP 200 with no
RUN_ERROR, where the published packages raise at endpoint.py:23.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Maxim